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There are no separate serial/SPI devices under the at91-usart MFD, but
actually the MFD is used as a serial or a SPI device. There are no DT
sub-nodes for the MFD children, so we should use platform device API to
register the drivers.
Suggested-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>